Anritsu 37 C Series, Руководство по эксплуатации, Страница: 184 / 603

8-5
ACTIVE DEVICE Active devices are key components in microwave systems.
The measurements that are made on active devices are similar to
those made on passive devices.
Active devices come in many shapes and sizes. In most cases we are
going to have to develop a fixture in which to mount the device.
Active devices require bias voltages, and in many cases they are easily
damaged. High gain amplifiers may saturate with input signals of
–50 dBm! With active devices, we have a new set of measurement re-
quirements.
The 373XXC has been designed to help you make these types of mea-
surements. It includes one 70 dB step attenuator (60 dB for 37377C
and 37397C) used to adjust the Port 1 power level. A second 40 dB step
attenuator is also included (with Option 6) in the forward transmis-
sion path to allow measurement of high gain devices without sacrific-
ing reverse transmission and reflection measurements (S
12
, S
22
). Bias
tees on each port are used to bias the device via the test port center
conductor. This approach to bias is useful for testing transistors; how-
ever, MMIC’s usually require bias injection at other points (Figure
8-19).
Test fixtures are necessary for mounting the device so that it can be
measured in our coaxial (or waveguide) measuring system (Figure
8-20).
ACTIVE DEVICE MEASUREMENTS
8-24 37XXXC OM
B i a s T e e s
R F
I N
T E S T
P O R T
V
B I A S
Figure 8-19. Bias Tee
ACTIVE DEVICES
FETs
Amplifiers
MMIC’s
COMMON MEASUREMENTS
S11 Input Match
S21 Gain
S12 Reverse Isolation
S22 Output Match
WHAT’S DIFFERENT?
Connectors
- There May Not Be Any
- Instead You Will See:
Tabs-Leads-Pads
WHAT’S DIFFERENT?
Voltage-Bias Requirements
Signal Level Performance
- Power Output
- Max Input Level
Non Linear
- Gain Compression